Hydraulic power transmission assemblies and fluid distribution systems may utilize a vane-type pump. Such pumps typically have a rotor with a plurality of circumferentially spaced vanes rotatably carried by the rotor and slidable relative thereto in slots provided in the rotor. The rotor and vanes cooperate with the internal contour of a containment ring or eccentric ring eccentrically mounted relative to an axis of the rotor and vanes to create fluid chambers between the containment ring or eccentric ring, rotor and vanes. Due to the eccentricity between the containment ring or eccentric ring and the rotor and vanes, the fluid chambers change in volume as they are moved with the rotating rotor and become larger in volume as they are moved across an inlet port and smaller in volume across an outlet port. To vary the eccentricity between the containment ring or eccentric ring and the rotor, the containment ring or eccentric ring may be pivoted upon a fixed axis in a pump housing. Pivoting the containment ring or eccentric ring varies the change in volume of the fluid chambers in use of the pump and hence, varies the displacement characteristic of the pump. A description of inherent problems with prior art pumps is set forth in the Background of Invention section of the above-referenced co-pending opposition U.S. Ser. No. 10/021,566. A description of an improved pump and method of control is set forth below.
While such a pump improves proper oil pressure and flow control, improvements in oil control are desired.
A typical internal combustion engine requires a certain flow rate of lubricating oil delivered within a certain range of pressure, the flow rate and pressure varying with the speed of crankshaft rotation, the engine temperature and the engine load. A fixed displacement pump operating at high speeds and at cold start conditions can produce excessively high oil pressures, and at high temperature and low speed conditions the oil pressure can be less than desired. Increasing the displacement of the oil pump to improve the oil pressure at high temperature and low speed conditions will consume more power at all conditions and will worsen the excessive oil pressure at high speed and low temperature conditions. It is desirable to provide improved control over conventional fixed displacement pumps that will operate at higher efficiency and optimizes pump output flow and pressure in accordance with engine speed and engine operating conditions.
Also, current energy conservation requirements for automotive equipment, coupled with increased pump displacements for actuation of variable cam/valve timing systems, demand more efficient engine lubrication system designs.